los bronces development project nelson sánchez; …existing copper production to a level of...

The Southern African Institute of Mining and Metallurgy Surface Mining 2008

N Sánchez, R Fiebig, P Perrier, A Vásquez

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Page 79

LOS BRONCES DEVELOPMENT PROJECT

Nelson Sánchez; Rolf Fiebig; Pierre Perrier; Alejandro Vásquez

ABSTRACT

The Los Bronces Development Project (LBDP) was approved in October 2007 by the

Anglo American plc Board at a capital cost of some US$1.74B, and is scheduled to be

completed by the end of 2010. The project represents a big step forward for the Los

Bronces mine since it will increase the treatment rate by 140%, the mining rate by 64%

and almost double copper production during the first four years of the project. This

economy of scale will also position Los Bronces as a much bigger and efficient mining

operation, better prepared to face adverse market scenarios and allowing Anglo to

consolidate its position in base metals.

The project addressed numerous scope alternatives such as plant capacity vs mine

capacity, cut-off grade strategy to maximise value based on the existing flotation and

leaching process, cutback strategy, etc.

Main infrastructure aspects of the project are as follows:

• Dump area with 2400Mt capacity for waste and low grade material

• Mining equipment: 1 x electric shovel, 12 x 300t trucks, 1 x drill

• Primary crusher: 60” x 89”

• Three new power lines (144MW capacity)

• Grinding plant at 87kt/day nominal capacity (includes a 4.3km tunnel with a

regenerative conveyor belt)

• Grinding plant: 1 SAG mill 40’ x 25’, 2 ball mills

• Slurry pipeline (52 km from grinding to flotation plant) with five choke stations

• Flotation plant (rougher, cleaning, regrinding circuits and molybdenum flotation).

The history of Los Bronces started in 1867 when it was discovered. In 1978 ENAMI

(Government company) sold Los Bronces to Exxon for US$112M. The same year a snow

avalanche destroyed San Francisco Flotation Plant. In 1979 the plant was rebuilt at

4.9kt/day and from 1979 to 2002 several plant expansions were made up to 54kt/day

capacity. In 2002 Anglo acquired Los Bronces for US$1.3B.



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The 2002 resource and reserve statement showed reserves at 459Mt at 1.02%CuT and

resources at 780Mt at 0.80%CuT. The 2007 statement shows reserves at 1,480Mt at

0.67%CuT and resources at 1,644Mt at 0.45%CuT.

Defining the size of a plant expansion is the key challenge that any expansionary project

faces. The scope of this paper is a general review of the project, describing all the mining

techniques that were used to define the best options that maximise value. In this context,

a range of plant capacities (from 58 to 230kt/day) combined with a range of mining

capacities (from 83 to 166Mt/a) were evaluated in detail, defining for each option a mine

plan, Capex and Opex, and cut-off grade strategy for flotation and leaching processes and

the associated Net Present Value (NPV) that was used as the selection criteria.

The Los Bronces mineral resources potential provides good growth opportunities for the

mine beyond LBDP implementation, offering an exciting invitation to continue studying

new initiatives that maximise the value of this deposit.

LOS BRONCES DEVELOPMENT PROJECT

1. Background

• Location

The Los Bronces operation is located in central Chile and is split between two sites

connected by an ore slurry pipeline.

The mine is located some 65km north-east of Santiago. Primary crushing, grinding, and

related infrastructure are sited adjacent to the open pit mining operation. Marginal grade

ore leaching is performed on dumps downstream of the mine site, where related solvent

extraction/electrowinning facilities are located.

The mine site is in the Andean Mountains and lies in an area of steep relief in the upper

reaches of the San Francisco Valley at an elevation of between 3400m above sea level

(masl) and 4100masl. Access is by public roads from Santiago.



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A 56km mostly buried pipeline runs from the Los Bronces grinding plant site to the

flotation facility at Las Tórtolas, traversing three tunnels while dropping in elevation

from 3450masl to 750masl.

Las Tórtolas is located in the Colina valley, some 40km north of Santiago. Access is via

the San Martin highway or the Pan-American highway from Santiago. The flotation plant

is situated in an open valley at an elevation of 750masl. Tailings impoundment is

adjacent to the plant site, using sand dams and taking advantage of favourable

topography.

The climate at Los Bronces is typical of the high Andes. Mean annual snowfall,

concentrated mostly in the winter period (April through September), is 764cm.

Temperatures range from -18ºC in winter to 19ºC in summer.

The climate at Las Tórtolas is temperate. Mean rainfall is 220mm/a and temperatures

vary from 0ºC in winter to 34ºC in summer.

P a c i f i c

O c e a n

CHILE

Santiago

A R G E N T I N A

LOS BRONCES MINE

CHAGRES SMELTER

LAS TORTOLAS

FLOTATION PLANT



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Page 82

• Strategic Considerations

The Anglo American plc Base Metals Division strategy is to achieve long term

sustainable maximisation of shareholder value through finding, acquiring, developing and

operating large, long life, low cost base metals businesses in a zero harm, socially and

environmentally responsible manner.

Within the framework of this strategy, it is the objective of the copper division to grow its

cost effective copper production from approximately 5% in 2005 to in excess of 7.5% of

world mine production over a 10 year time horizon. This implies more than doubling

existing copper production to a level of approximately 1.5Mt/a.

Los Bronces is one of Anglo Base’s existing two world class operations. Doubling

production at Los Bronces is consistent with and the first step in the achievement of the

copper division growth strategy (the Collahuasi expansions, Quellaveco and Michiquillay

are the other assets which are included in the current strategic growth plan).

The long term prospects for the copper industry are particularly positive. Although

current prices are presently far in excess of the long term equilibrium levels and

unsustainable, a period of above average demand growth is being experienced and

supply/demand fundamentals are, for the foreseeable future, more favourable than have

been seen for some considerable period of time.

2. Project Description

An investment of US$1,744M (nominal) was proposed for an 87kt/day expansion to the

sulphide ore treatment capacity at the Los Bronces operation.

The expansion will increase the ore treatment rate from 61kt/day (base case) to

148kt/day. Average production of fine copper in concentrates (2011-2020) will be about

380kt/a, twice that forecast for the base case (2007 life of mine (LOM) forecast).

The proposed investment covers the following scope:

• Mining Fleet: Addition of 1 x 73yd3

electric shovel, 12 x 300t capacity haul

trucks, 1 x 10⅝” drill rig and support equipment (bulldozer, wheel dozer, water

truck, etc.) to increase mine capacity from 84 to 128Mt/a (including the

incremental 87kt/day ore).



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• Primary Crushing: A modified 60” x 89” (1000hp) primary crusher, to

complement an identical unit currently under construction for the existing

operation.

• Coarse Ore Transport: A downhill, regenerative conveyor system for coarse ore.

The conveyor will traverse a route that includes a new 4km tunnel connecting Los

Bronces with the new grinding plant site at Confluencia.

• Grinding Plant: Coarse ore stockpile, conventional semi-autogenous grinding

circuit, ore thickeners and ore slurry preparation tanks. The new plant will

operate concurrently with the existing grinding plant at Los Bronces.

• Ore Slurry Transport: A new, 28” diameter, 51km long pipeline, installed along

the existing ore slurry pipeline route to Las Tórtolas.

• Flotation: New copper and molybdenum flotation equipment at Las Tórtolas

(near the existing flotation plant).

• Tailings: Tailings thickener, transport systems (pumps, pipelines and flumes),

cyclone station expansion and modification, extensions to sand dam drainage and

new borrow dams consistent with a design to achieve ultimate tailings

impoundment capacity of 2,100Mt.

• Water Supply: Expansion of pump stations and pipelines to increase capacity to

recirculate process water from Las Tórtolas to Confluencia. Expansion to fresh

water intake and pump system in the Riecillos valley.

• Power Supply: Additional high-tension supply lines, two new substations and

modifications to existing power lines and substations

The project was approved in October 2007, with advanced commitment for critical path

grinding equipment and interim engineering. On this basis, project start-up is forecast in

January 2011.



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Figure 1: General layout of main expansion areas

3. Mining Design

3.1 Terms of Reference

Mine design starts with the Terms of Reference, which include:

• Minimum life of mine required for the company for a feasible expansion.

• Long term price forecasts of main products and consumables.

• Preliminary estimates of operating costs, fixed and variable, for indexation to

associate with different plant treatment and mining capacities.

• Block model with copper and molybdenum grades.

• Mining and property restrictions.

• Geotechnical design criteria.

• Geometallurgical parameters: copper recovery, copper concentrate grade,

plant treatment rate (dependent on rock hardness), molybdenum recovery, etc.

• Area for waste dumps and tailings dam.

• Technology to be used, size and type of mining equipment, primary crusher,

grinding, flotation, etc.

LAS TORTOLAS

(750 msal)

VIZCACHAS

TUNNEL

CONFLUENCIA

ORTIGA TUNNEL

28” SLURRY PIPELINE

EMERGENCY POND

CHOKE STATION

HOLDING TANKCS 0A

CS 1A

CS 2A

CS 3A

Laguna Seca

Discharge

Box

EL DURAZNO BRIDGE

CS 1.5A

COLINA BRIDGEBy Pass Peldehue

LOS

BRONCES

(3450 masl)

From Confluencia 51 km

LAS TORTOLAS

(750 msal)

VIZCACHAS

TUNNEL

CONFLUENCIA

ORTIGA TUNNEL


EMERGENCY POND

CHOKE STATION

HOLDING TANK


EMERGENCY POND

CHOKE STATION

HOLDING TANKCS 0A

CS 1A

CS 2A

CS 3A

Laguna Seca

Discharge

Box

EL DURAZNO BRIDGE

CS 1.5A

COLINA BRIDGEBy Pass Peldehue

LOS

BRONCES

(3450 masl)

From Confluencia 51 km



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Page 85

3.2 Mine Design

Based on the Terms of Reference and always considering the answer to the main question

“Which is the optimum expansion?”, various options of possible expansions in plant

treatment rate and associated mining capacity were designed, considering existing

technology.

The determination of the optimal expansion was developed during the pre-feasibility

study, allowing the analysis in detail of only the optimal case in the feasibility study, with

some sensitivities.

The pre-feasibility study considered that, based on the types of grinding system available

in the market, a new grinding plant could add between 15 and 120kt/day to the existing

plant capacity. Thus the Los Bronces plant could reach a total treatment rate in the range

75 to 180kt/day. The higher capacity was the maximum possible expansion due to

restrictions of minimum mine life associated with the existing ore reserves at the time of

the study.

For each plant capacity option, mine plan alternatives were analysed to determine the

mining capacity and the copper cut-off grade strategy that maximised the Net Present

Value NPV) in each case. Figure 2 depicts the sequence that was followed to obtain the

NPV for each mine-plant combination.



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6

Figure 2: Design & evaluation stages for each Mine-Plant combination

3.3 Final Pit Selection, Mine Extraction Sequence (Phases)

For each mine-plant alternative, the final pit and optimum reserve extraction sequence

were determined (volume of resources economically exploitable). The basis for the

optimisations were economic (given long term metal price forecasts, operating costs,

associated initial and replacement capital expenditures) and technical ( grade model,

metallurgy, geotechnical parameters, etc).

The Whittle software used in this task applies the Lerchs & Grossman optimisation

algorithm. For final pit limit selection, Whittle analyses the incremental NPV according

to the methodology shown in Figure 3.

Final Pit

Pushback selection

Accesses and pushbacks design

Mine and plant alternatives definition

Cut off grade strategy (by Opticut / COMET– K. Lane)

Mining plans (by Mine-sight / M821)

Fine Cu and Mo production

Equipment fleet calculation, labor, operation cost and

investment.

Economic evaluation

(NPV - RRI - ROCE)

Optimal alternative

selection

Design parameters (Slope

Angle,...)

Block Model (CuT, MoT, CC, etc)

Initial Topography

Metallurgical parameters

Economic model

Optimal mining sequence definition

Rutine

Lersch &

Grossman

Mining Plans, production level, Cost and investment

Whittle

Mine-Sight

Datamine

Terms of reference

Final Pit

Pushback selection

Accesses and pushbacks design

Mine and plant alternatives definition

Cut off grade strategy (by Opticut / COMET– K. Lane)

Mining plans (by Mine-sight / M821)

Fine Cu and Mo production

Equipment fleet calculation, labor, operation cost and

investment.

Economic evaluation

(NPV - RRI - ROCE)

Optimal alternative

selection

Design parameters (Slope

Angle,...)

Block Model (CuT, MoT, CC, etc)

Initial Topography

Metallurgical parameters

Economic model

Optimal mining sequence definition

Rutine

Lersch &

Grossman

Rutine

Lersch &

Grossman

Mining Plans, production level, Cost and investment

Whittle

Mine-Sight

Datamine

Terms of referenceTerms of reference



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Page 87

Figure 3: Final pit shell selection

Taking into consideration the size and operational constraints of the selected equipment

and the desired production level, the design process was carried out in phases up to the

final pit design, including the required access ramps. The project used MineSight

software in this design stage, and the result of this work is presented in Figure 4.

VAN

INCREMENTAL

PIT’sRev F=1

#

Elegido

Rango de pit’s que nos interesa analizar

Zona de elección

del Pit Óptimo

BestCase

Wors

t Cas

e

Specified

Case

•Best Case: Pit by pit extraction until

f inal pit.

•Worst Case: Bench by bench until

f inal pit wall, extraction.

•Specified Case: is defined, thinking in

a possible extraction and treatment

rate. This gives a more realistic case

then the best ore the worst case.

Incremental NPV graphic:In

cre

me

nta

l

NP

V

Area of the optimal

pit criteria

Pit range of interest

VAN

INCREMENTAL

PIT’sRev F=1

#

Elegido

Rango de pit’s que nos interesa analizar

Zona de elección

del Pit Óptimo

BestCase

Wors

t Cas

e

Specified

Case

•Best Case: Pit by pit extraction until

f inal pit.

•Worst Case: Bench by bench until

f inal pit wall, extraction.

•Specified Case: is defined, thinking in

a possible extraction and treatment

rate. This gives a more realistic case

then the best ore the worst case.

Incremental NPV graphic:In

cre

me

nta

l

NP

V

Area of the optimal

pit criteria

Pit range of interest



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Page 88

Figure 4: Design of operational phases

3.4 Definition / Determination of the Optimal Expansion

Opti-Cut software, based on Kenneth F. Lane theory, was used to optimise cash flows

depending on the mine and plant capacities, through adjusting cut-off grades for the ore

feed to the grinding plant. Considering the design phases, the maximum NPV was

calculated for different combinations of mining capacity and ore fed to the grinding plant.

The NPVs from these analyses were used as a guideline for more detailed study of the

most economically attractive options. These cases required the development of detailed

mine plans and related economic analysis using the company’s financial model.

Table 1 and Graph 1 show the combinations of plant treatment rate and mining capacity

studied.



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Page 89

Table 1: Matrix of Mine-Plant combinations

Capacidades Plantas

22

(58 KTPD)

33

(90 KTPD)

44

(120 KTPD)

49

(135 KTPD)

66

(180 KTPD)

84

(230 KTPD)

Ca

pa

cid

ad

es

Min

a(M

ton

/añ

o)

83

(227 KTPD)

91

(250 KTPD)

99

(270 KTPD)

110

(300 KTPD)

128

(350 KTPD)

•Estimación Preliminar del VAN

de cada combinación

Uso de Teoría de K. Lane

(Determinar el mejor VAN dadas las máximas

capacidades Mina y Planta definidas - OPTICUT)

Sulfuros

(MTPA)

Cátodos

(Kton Cu Fino año)

XXXX XX XX XX XX

146

(400 KTPD)

166

(450 KTPD)

Capacidades Plantas

22

(58 KTPD)

33

(90 KTPD)

44

(120 KTPD)

49

(135 KTPD)

66

(180 KTPD)

84

(230 KTPD)

Ca

pa

cid

ad

es

Min

a(M

ton

/añ

o)

83

(227 KTPD)

91

(250 KTPD)

99

(270 KTPD)

110

(300 KTPD)

128

(350 KTPD)









Sulfuros

(MTPA)

Cátodos

(Kton Cu Fino año)

XXXX XX XX XX XX

146

(400 KTPD)

166

(450 KTPD)

Mill Capacities

Sulphide

Cathode

(Kton Fine CU year)

Min

e C

ap

ac

itie

s (M

to

n/ye

ar)

Preliminary NPV estimation for

every combination mine-mill

Use of K. Lane Theory

(Best NPV determination based on maximun mill and

mine capacities – OPTICUT)

Capacidades Plantas

22

(58 KTPD)

33

(90 KTPD)

44

(120 KTPD)

49

(135 KTPD)

66

(180 KTPD)

84

(230 KTPD)

Ca

pa

cid

ad

es

Min

a(M

ton

/añ

o)

83

(227 KTPD)

91

(250 KTPD)

99

(270 KTPD)

110

(300 KTPD)

128

(350 KTPD)






Sulfuros

(MTPA)

Cátodos

(Kton Cu Fino año)

XXXX XX XX XX XX

146

(400 KTPD)

166

(450 KTPD)

Capacidades Plantas

22

(58 KTPD)

33

(90 KTPD)

44

(120 KTPD)

49

(135 KTPD)

66

(180 KTPD)

84

(230 KTPD)

Ca

pa

cid

ad

es

Min

a(M

ton

/añ

o)

83

(227 KTPD)

91

(250 KTPD)

99

(270 KTPD)

110

(300 KTPD)

128

(350 KTPD)









Sulfuros

(MTPA)

Cátodos

(Kton Cu Fino año)

XXXX XX XX XX XX

146

(400 KTPD)

166

(450 KTPD)

Mill Capacities

Sulphide

Cathode

(Kton Fine CU year)

Min

e C

ap

ac

itie

s (M

to

n/ye

ar)

Preliminary NPV estimation for

every combination mine-mill

Use of K. Lane Theory

(Best NPV determination based on maximun mill and

mine capacities – OPTICUT)



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Page 90

Graph 1: Final NPV for the different combinations

3.5 Plant Capacity Definition

After this extensive analysis it was determined that, under the defined Terms of

Reference, the best mine-plant combination for Los Bronces was 132Mt/a total mining

capacity and 54Mt/a treatment at the sulphide plant, resulting in an increase in fine

copper production from an average of 220kt/a to 400kt/a.

Graph 2 compares the mining and plant treatment rates, copper grades and copper cut-off

grades for the Los Bronces Base Case and the Optimum plan, the Los Bronces

Development Project plan.

Resultados Opti Cut

(VAN MUS$)

700

900

1100

1300

1500

58 90 120 135 180 230

Tratamiento Planta (KTPD)

VA

N (M

US

$)

227 270 300 350 400 450

M T P A 2 1 3 3 4 4 4 9 6 6 8 4

M T P A K T P D K T P D 5 8 9 0 1 2 0 1 3 5 1 8 0 2 3 0

8 3 2 2 7 1 0 3 5 1 1 9 2 1 0 8 3 1 0 1 0 8 2 9

9 9 2 7 0 9 6 2 1 2 0 2 1 2 8 1 1 2 7 9 1 0 5 5 7 7 6

1 1 0 3 0 0 9 6 9 1 1 4 5 1 3 2 1 1 2 7 3 1 2 0 4 9 2 6

1 2 8 3 5 0 9 6 9 1 2 1 1 1 3 4 9 1 3 6 0 1 4 0 5 1 1 3 4

1 4 6 4 0 0 9 7 3 1 1 5 8 1 3 3 9 1 3 6 5 1 5 0 5 1 3 0 4

1 6 6 4 5 0 9 0 9 1 1 7 8 1 3 1 5 1 4 0 4 1 5 3 0 1 4 7 4

T r a t a m i e n t o P l a n t a

M o v i m i e n t o M i n a

Movimiento

Mina

Casos de Mayor

interés 1

Casos de Mayor

interés 2

Resultados Opti Cut

(VAN MUS$)

700

900

1100

1300

1500

58 90 120 135 180 230


VA

N (M

US

$)

227 270 300 350 400 450

M T P A 2 1 3 3 4 4 4 9 6 6 8 4

M T P A K T P D K T P D 5 8 9 0 1 2 0 1 3 5 1 8 0 2 3 0

8 3 2 2 7 1 0 3 5 1 1 9 2 1 0 8 3 1 0 1 0 8 2 9

9 9 2 7 0 9 6 2 1 2 0 2 1 2 8 1 1 2 7 9 1 0 5 5 7 7 6

1 1 0 3 0 0 9 6 9 1 1 4 5 1 3 2 1 1 2 7 3 1 2 0 4 9 2 6

1 2 8 3 5 0 9 6 9 1 2 1 1 1 3 4 9 1 3 6 0 1 4 0 5 1 1 3 4

1 4 6 4 0 0 9 7 3 1 1 5 8 1 3 3 9 1 3 6 5 1 5 0 5 1 3 0 4

1 6 6 4 5 0 9 0 9 1 1 7 8 1 3 1 5 1 4 0 4 1 5 3 0 1 4 7 4



Movimiento

Mina

Casos de Mayor

interés 1

Casos de Mayor

interés 2

NPV Results

(MUS$)

Mayor interest

cases 1

Plant Treatment (KTPD)

NP

V (M

US

$)

Mine

Movement

Mine Movement

Plant Movement

Mayor interest

cases 2

Resultados Opti Cut

(VAN MUS$)

700

900

1100

1300

1500

58 90 120 135 180 230


VA

N (M

US

$)

227 270 300 350 400 450

M T P A 2 1 3 3 4 4 4 9 6 6 8 4

M T P A K T P D K T P D 5 8 9 0 1 2 0 1 3 5 1 8 0 2 3 0

8 3 2 2 7 1 0 3 5 1 1 9 2 1 0 8 3 1 0 1 0 8 2 9

9 9 2 7 0 9 6 2 1 2 0 2 1 2 8 1 1 2 7 9 1 0 5 5 7 7 6

1 1 0 3 0 0 9 6 9 1 1 4 5 1 3 2 1 1 2 7 3 1 2 0 4 9 2 6

1 2 8 3 5 0 9 6 9 1 2 1 1 1 3 4 9 1 3 6 0 1 4 0 5 1 1 3 4

1 4 6 4 0 0 9 7 3 1 1 5 8 1 3 3 9 1 3 6 5 1 5 0 5 1 3 0 4

1 6 6 4 5 0 9 0 9 1 1 7 8 1 3 1 5 1 4 0 4 1 5 3 0 1 4 7 4



Movimiento

Mina

Casos de Mayor

interés 1

Casos de Mayor

interés 2

Resultados Opti Cut

(VAN MUS$)

700

900

1100

1300

1500

58 90 120 135 180 230


VA

N (M

US

$)

227 270 300 350 400 450

M T P A 2 1 3 3 4 4 4 9 6 6 8 4

M T P A K T P D K T P D 5 8 9 0 1 2 0 1 3 5 1 8 0 2 3 0

8 3 2 2 7 1 0 3 5 1 1 9 2 1 0 8 3 1 0 1 0 8 2 9

9 9 2 7 0 9 6 2 1 2 0 2 1 2 8 1 1 2 7 9 1 0 5 5 7 7 6

1 1 0 3 0 0 9 6 9 1 1 4 5 1 3 2 1 1 2 7 3 1 2 0 4 9 2 6

1 2 8 3 5 0 9 6 9 1 2 1 1 1 3 4 9 1 3 6 0 1 4 0 5 1 1 3 4

1 4 6 4 0 0 9 7 3 1 1 5 8 1 3 3 9 1 3 6 5 1 5 0 5 1 3 0 4

1 6 6 4 5 0 9 0 9 1 1 7 8 1 3 1 5 1 4 0 4 1 5 3 0 1 4 7 4



Movimiento

Mina

Casos de Mayor

interés 1

Casos de Mayor

interés 2

NPV Results

(MUS$)

Mayor interest

cases 1

Plant Treatment (KTPD)

NP

V (M

US

$)

Mine

Movement

Mine Movement

Plant Movement

Mayor interest

cases 2



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Page 91

Graph 2: Mining rate, plant treatment, copper grade, cut off grade: Base case vs.

4. Future of the Los Bronces Mine District

As discussed earlier, the Los Bronces Development Project defined the best expansion

option according to the Terms of Reference and reserves available at the time.

During the course of this study, the mine has continued with a core drilling campaign in

the boundaries of the operation, increasing the available resources around the pit. This

could eventually support further expansions, giving Los Bronces a very bright future.



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los bronces development project nelson sánchez; …existing copper production to a level of...

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